Image transmitter

ABSTRACT

An image transmitter has: an encoder for receiving image data and outputting coded image data; a packet transmitter for receiving the coded image data from the encoder, buffering the coded image data while counting a data number, and when coded image data of one packet of a fixed length is buffered, packetizing the coded image data and transmitting the packetized coded image data; a first enable signal generator for generating a first enable signal which becomes enable at a start of transmission of each packet and disable at an end of transmission; and a second enable signal generator for generating a second enable signal which becomes enable at a start of transmission of a predetermined number of packets and disable at an end of transmission. The image transmitter and image transmitting method are provided which can transmit image data to an application chip fabricated on the assumption that it receives a packet of a fixed data number and a frame of a fixed packet number.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and claims priority of Japanese PatentApplication No. 2005-076192 filed on Mar. 17, 2005, the entire contentsof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

A) Field of the Invention

The present invention relates to an image transmitter, and moreparticularly to an image transmitter for transmission of moving imagesor the like which variable-length compresses input image data andsequentially transmits compressed image information.

B) Description of the Related Art

Digital image information is widely used because of propagation ofdigital cameras. Image information has a large information quantity sothat data compression processing is performed for data storage andcommunications. JPEG and the like are prevailing as compressionprocessing for image information. Data compression processing of JPEG isperformed by using pixel groups of 8×8, 16×16 and the like as a basicunit. For 8×8 and 16×16 pixel groups, process units are 8 rows and 16rows, respectively. This process unit is also called a macro block whereappropriate. Data compression is performed after a macro block of 8 or16 rows is input. JPEG compression outputs variable length data.

Generally, an image transmitter compresses input image data, stores thecompressed coded data in a frame memory, and transmits it afternecessary processes are executed. Most of application chips forreceiving coded image data and decoding it for display or the like arefabricated on the assumption that a packet is made of a predetermineddata number (hereinafter called a fixed data number) and a frame (fixedlength frame) constituted of a predetermined number of packets (fixedpacket number) is received. Since an encoding process generates variablelength coded data, it cannot be transmitted unless proper processes areexecuted. It has been proposed that if coded data buffered in the framememory is smaller than the predetermined data length, dummy data isadded to the coded data to form a fixed length frame.

FIGS. 3A and 3B are a block diagram realizing an embodiment ofJP-A-2002-247577 and its data format.

Referring to FIG. 3A, a camera 51 acquires moving image data at apredetermined time interval, and sequentially inputs it to an imageencoder 52. The image encoder 52 encodes (digitalizes) the input movingimage data of each macro block and variable-length encodes it to removeredundancy. Moving image data variable-length encoded by the imageencoder 52 is sent to a frame separator circuit 53 via a data line Ii ata transmission rate varying at each moving image (frame) data. The frameseparator circuit 53 forms a frame having a predetermined constant datalength from the input moving image data varying its data length (havinga different data length) each time it is input, and outputs the frame toa data line Iii.

FIG. 3B shows a frame format having a constant data length. One frame isconstituted of T bytes. A top field includes a sync word SW of one byteand a valid data number BN of one byte, of moving image data. Therefore,the remaining number of bytes is T−2. If the moving image data 63 has xbytes, dummy data 64 of T−x−2 is added. In this manner, a frame having aconstant data length T is formed by adding the dummy data. If the datalength of moving image data is longer than the data length capable ofbeing inserted in one frame, the moving image data in excess of theconstant data length is discarded. A modulator 54 modulates an inputframe by a predetermined modulation scheme and sends it out to atransmission line at a constant transmission rate.

A demodulator 55 receives a frame transmitted via the transmission line,demodulates it, and supplies it to a data reproduction circuit 56 via adata line IIi. The data reproduction circuit 56 performs framesynchronization by detecting the sync word SW from each input frame, anddetects the valid data number BN from each received frame. The datareproduction circuit 56 extracts moving image data 63 of the valid datanumber BN from the frame data excluding the sync word SW and valid datanumber BN. The extracted moving image data 63 is supplied to an imagedecoder 57 via a data line IIii. The image decoder 57 decodes movingimage data and sends decoded moving image data to a monitor 58. Themonitor 58 displays the moving image.

A frame memory is used for buffering coded data of one frame and addingdummy data to form frame data of a constant length. A data amount ofimage data of one frame is large not negligible even if the image datais compressed data, and the capacity of the frame memory is notnegligible.

SUMMARY OF THE INVENTION

An object of this invention is to provide an image transmitter withoutusing a frame memory, and being capable of transmitting a frame to anapplication chip fabricated on the assumption that it receives a packetof a fixed data number and a frame of a fixed packet number.

Another object of this invention is to provide an image transmittingmethod without using a frame memory, and being capable of transmitting aframe to an application chip fabricated on the assumption that itreceives a packet of a fixed data number and a frame of a fixed packetnumber.

According to one aspect of the present invention, there is provided animage transmitter comprising: an encoder for receiving image data andoutputting coded image data; a packet transmitter for receiving thecoded image data from the encoder, buffering the coded image data whilecounting a data number, and when coded image data of one packetcorresponding to a fixed data number is buffered, packetizing the codedimage data and transmitting the packetized coded image data; a firstenable signal generator for generating a first enable signal whichbecomes enable at a start of transmission of each packet and disable atan end of transmission; and a second enable signal generator forgenerating a second enable signal which becomes enable at a start oftransmission of packets of a fixed packet number and disable at an endof transmission.

According to another aspect of the present invention, there is providedan image transmitting method comprising: an encoding step of receivingimage data and outputting coded image data; a packet transmitting stepof receiving the coded image data, buffering the coded image data whilecounting a data number, and when coded image data of one packetcorresponding to a fixed data number is buffered, packetizing the codedimage data and transmitting the packetized coded image data; a firstenable signal generating step of generating a first enable signal whichbecomes enable at a start of transmission of each packet and disable atan end of transmission; and a second enable signal generating step ofgenerating a second enable signal which becomes enable at a start oftransmission of packets of a fixed packet number and disable at an endof transmission.

Instead of using an enable signal representative of a data length of oneframe, a different enable signal is generated which becomes enable atthe start of transmission of a predetermined number of packets anddisable at the end of transmission of the predetermined number ofpackets, the end being detected by counting the packets. It is thereforepossible for an application chip to receive coded image data. Although aset of received coded data packets is a data group different from thedata in the original frame, the application chip can adjust the receivedcoded data and demodulate an image of each frame.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the structure of an image transmitteraccording to an embodiment of the invention.

FIGS. 2A, 2B and 2C are a timing chart showing timings of varioussignals in the image transmitter shown in FIG. 1, and diagrams showingdata format of the last packet of a frame.

FIGS. 3A and 3B are a block diagram showing the structure of an imagetransmitter according to prior art and a diagram showing frame dataformat of image data.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

If an image transmitter for compressing image data and transmitting itcan omit a frame memory, the structure can be simplified, a chip areacan be reduced and a production cost can be reduced. However, if encodedvariable length image data is to be transmitted at a fixed data length,it is necessary not only to add dummy data to the last packet ifnecessary after the last macro block is encoded, in order to packetizeit, but also to generate dummy packets if the number of packets isinsufficient. It is not always possible to encode the last macro blockand further perform such processes after the last macro block isencoded. It is therefore very difficult to omit the frame memory.

FIG. 1 is a block diagram showing the configuration of an imagetransmission system according to an embodiment of the present invention.A camera 1 supplies image data or the like to an image transmitter 3,and the image transmitter 3 supplies coded image data to an applicationchip 5. The application chip 5 writes the received image data in a framememory 7 to use it for desired applications. In the following,description will be made on each constituent component, and the imagetransmitter 3 among others will be described in detail.

The camera 1 acquires moving image data at a predetermined timeinterval, and supplies the image data together with a horizontal syncsignal H.SYNC and a vertical sync signal V.SYNC to an image encoder 31of the image transmitter 3.

The image encoder 31 encodes input image data by JPEG-compression andstores it in a one packet memory 32 having one packet capacity. Ascompared to the capacity of one frame, the capacity of one packet isvery small. The one packet memory 32 buffers the supplied coded imagedata. An in-packet data number counter 33 is connected to the one packetmemory 32. The in-packet data number counter 33 counts the number ofcoded data buffered in the one packet memory 32. The data number issupplied from the in-packet data number counter 33 to an in-packet dummydata adder 35.

When the number of data buffered in the one packet memory 32 reaches anin-packet fixed data number, the one packet memory 32 outputs packetizedcoded data CD to an output line T32. The in-packet data number counter33 supplies a first enable signal EN1 to the output line T33 and apacket number counter 34. The first enable signal EN1 rises at the startof transmission of one packet coded data and falls at the end of thetransmission.

The packet number counter 34 receives and counts the first enable signalEN1 and supplies a second enable signal EN2 to an output line T34. Thesecond enable signal EN2 rises at the start of transmission of a firstpacket and falls at the end of transmission of the packet correspondingto the last of the assumed fixed number of packets (for simplicity, 8packets are assumed) in a frame on the assumption of which number theapplication chip is fabricated. Since the second enable signal isgenerated depending upon the packet number, the second enable signalbecomes an enable signal independent from the start and end of a frame.

Image data supplied from the camera 1 is in the unit of frame. Whenimage data of one frame is encoded, the image encoder 31 generates anencoding end signal and a code number of coded data and supplies them toan in-packet dummy data adder 35 and a CPU 37. When the coding of oneframe has finished, if the number of coded data buffered in the onepacket memory 32 does not reach the in-packet fixed data number, thecoded data stored in the one packet memory 32 is not allowed to betransmitted. The in-packet dummy data adder 35 is provided fortransmitting the last packet of a frame. The in-packet dummy data adder35 receives the data number from the in-packet data number counter 33and supplies the one packet memory 32 with dummy data of the number ofdata being short for constituting the last packet, to make the packet inone packet memory 32 a complete packet, which is then transmitted as thelast packet in the frame.

CPU 37 outputs frame data FD to an output line T38 via an I2C block 38.The frame data FD contains the encoding end signal of image data of oneframe and the number of coded data in the frame. In this case, if thepacket number does not reach the fixed packet number, the packet numbercounter 34 maintains the second enable signal high. CPU 37 can alsochange set values such as the fixed data number and fixed packet number.

As image data of the next frame is supplied from the camera 1, the imageencoder 31 starts new encoding. The one packet memory 32, in-packet datanumber counter 33 and packet number counter 34 continue operationssimilar to those described above. The second enable signal falls afterthe number of first enable signals EN1 counted by the packet numbercounter 34 reaches the fixed packet number.

The application chip 5 receives each packet having the fixed data numberwhile the first enable signal is high, and receives the packets of thefixed packet number while the second enable signal is high. The receivedcoded image data is written in the frame memory 7.

The operation in the unit of frame is performed by each of the camera 1,image encoder 31, in-packet data number counter 35, CPU 37 and I2C block38. The packet number counter 34 performs an enable signal generatingoperation in the unit of predetermined packet number, independently fromthe frame. Therefore, a frame end timing is generally different from thetiming of the second enable signal EN2 indicating transmission of apredetermined set of packets. The application chip 5 receives a packetof coded data CD of the fixed data number, and receives a set of packetsof the fixed packet number indicated by the second enable signal EN2.Therefore, the application chip can receive the coded data and write itin the frame memory 7. In addition, since the application chip 5receives information on each frame as the frame data FD, it can separatecoded image data written in the frame memory 7 and reconfigure it as aframe.

FIG. 2A is a timing chart illustrating the operation of the imagetransmitter 3 shown in FIG. 1. The coded data CD shown at the uppermostrow illustrates the state in which input image signals are encoded andoutput as packets of the fixed data number. The first frame F1 has fivepackets, the next frame F2 has seven packets, and the second next frameF3 has four packets. The last packet in each frame is represented by FE.

The first enable signal EN1 shown at the second row is an enable signalwhich becomes high at the start of transmission of each packet and lowat the end of the transmission. In the example shown in FIG. 2A, thesecond enable signal EN2 shown at the third row is an enable signalwhich becomes high at the start of transmission of eight packets, whichis the fixed packet number, and becomes low at the end of thetransmission. By using these enable signals EN1 and EN2, the applicationchip 5 receives the coded data CD by judging as if fixed length framedata in the unit of 8 packets is input. In the above description,although the enable signals become enable at a high level and disable ata low level, they may be inverted to become disable at the high leveland enable at the low level.

The frame data FD shown at the lowermost row is generated after the endof transmission of the last packet of each frame and transmitsinformation such as the coded data number. This information is used forprocessing received coded image data after the second enable signal EN2falls.

In the embodiment described above, when image data of one frame isencoded and if the number of data buffered in the one packet memory issmaller than the in-packed fixed data number, the dummy data adder 35adds dummy data to complete a packet. Since the coded image data of oneframe starts always from the start of a packet, subsequent processes canbe performed easily.

FIG. 2B is a schematic diagram showing the contents of the last packetFE in which the stored coded data is short of the predetermined datanumber, and dummy data is added to complete the packet. Thepredetermined data number Lpk includes real coded data RCD and dummycoded data DCD.

If data of two frames mixed in one packet can be processed, a packetcoupling the end of a preceding frame and the start of a succeedingframe may be formed without adding dummy data. In this case, the dummydata adder 35 may be omitted. The preceding frame is exchanged to thesucceeding frame at the midst of one packet.

FIG. 2C shows an example of a packet constituted of the last packet ofan i-th frame, whose real coded data RCD (Fi) is smaller than the fixeddata number, and real coded data RCD (Fi+1) of the next frame. In thiscase, the packet of coded data belongs to two frames. The frame data FDgenerated after the end of one frame, is generated independently fromthe packet period. However, there is no practical problem because theframe data is transmitted via the dedicated output line T38.

In the above description, the I2C block 38 outputs the frame data afterimage data of one frame is encoded. This transmission function may beomitted. In this case, headers indicating the start and end of a frameare added to coded data itself.

The present invention has been described in connection with thepreferred embodiments. The invention is not limited only to the aboveembodiments. It will be apparent to those skilled in the art that othervarious modifications, improvements, combinations, and the like can bemade.

1. An image transmitter comprising: an encoder for receiving image dataand outputting coded image data; a packet transmitter for receiving thecoded image data from said encoder, buffering the coded image data whilecounting a data number, and whcoded image data of one packetcorresponding to a fixed data number is buffered, packetizing the codedimage data and transmitting the packetized coded image data; a firstenable signal generator for generating a first enable signal whichbecomes enable at a start of transmission of each packet and disable atan end of transmission; and a second enable signal generator forgenerating a second enable signal which becomes enable at a start oftransmission of packets of a fixed packet number and disable at an endof transmission.
 2. The image transmitter according to claim 1, whereinsaid second enable signal generator receives and counts said firstenable signal to generate said second enable signal.
 3. The imagetransmitter according to claim 1, further comprising a dummy data adderfor adding dummy data, in a state that said encoder outputs coded imagedata of one frame to said packet transmitter and the number of data in alast packet is smaller than the fixed data number, to the data in thelast packet.
 4. The image transmitter according to claim 1, wherein saidencoder outputs information including an encoding end and a coded datanumber of a frame after said encoder encodes image data of a frame. 5.The image transmitter according to claim 4, further comprising acommunication function unit for receiving said information from saidencoder and transmitting frame data including the coded data number ofthe frame.
 6. The image transmitter according to claim 2, furthercomprising a dummy data adder for adding dummy data, in a state thatsaid encoder outputs coded image data of one frame to said packettransmitter and the number of data in a last packet is smaller than thefixed data number, to the data in the last packet.
 7. The imagetransmitter according to claim 2, wherein said encoder outputsinformation including an encoding end and a coded data number of a frameafter said encoder encodes image data of a frame.
 8. The imagetransmitter according to claim 7, further comprising a communicationfunction unit for receiving said information from said encoder andtransmitting frame data including the coded data number of the frame. 9.The image transmitter according to claim 3, wherein said encoder outputsinformation including an encoding end and a coded data number of a frameafter said encoder encodes image data of a frame.
 10. The imagetransmitter according to claim 9, further comprising a communicationfunction unit for receiving said information from said encoder andtransmitting frame data including the coded data number of the frame.11. An image transmitting method comprising: an encoding step ofreceiving image data and outputting coded image data; a packettransmitting step of receiving the coded image data, buffering the codedimage data while counting a data number, and when coded image data ofone packet corresponding to a fixed data number is buffered, packetizingthe coded image data and transmitting the packetized coded image data; afirst enable signal generating step of generating a first enable signalwhich becomes enable at a start of transmission of each packet anddisable at an end of transmission; and a second enable signal generatingstep of generating a second enable signal which becomes enable at astart of transmission of packets of a fixed packet number and disable atan end of transmission.
 12. The image transmitting method according toclaim 11, wherein said second enable signal generating step receives andcounts said first enable signal to generate said second enable signal.13. The image transmitting method according to claim 11, furthercomprising a dummy data adding step of adding dummy data, in a statethat said encoding step outputs coded image data of one frame and thenumber of data in a last packet is smaller than the fixed data number,to the data in the last packet.
 14. The image transmitting methodaccording to claim 11, wherein said encoding step outputs informationincluding an encoding end and a coded data number of a frame after saidencoding step encodes image data of a frame.
 15. The image transmittingmethod according to claim 14, further comprising a communication step ofreceiving said information and transmitting frame data including thecoded data number of the frame.
 16. The image transmitting methodaccording to claim 12, further comprises a dummy data adding step ofadding dummy data, in a state that said encoder outputs coded image dataof one frame and the number of data in a last packet is smaller than thefixed data number, to the data in the last packet.
 17. The imagetransmitting method according to claim 12, wherein said encoding stepoutputs information including an encoding end and a coded data number ofa frame after said encoding encodes image data of a frame.
 18. The imagetransmitting method according to claim 17, further comprising acommunication step of receiving said information and transmitting framedata including the coded data number of the frame.
 19. The imagetransmitting method according to claim 16, wherein said encoding stepoutputs information including an encoding end and a coded data number ofa frame after said encoding step encodes image data of a frame.
 20. Theimage transmitting method according to claim 19, further comprising acommunication step of receiving said information and transmitting framedata including the coded data number of the frame.